While a disc apparatus is at rest, an actuator including a head support arm having a head is held at a predetermined area (parking zone) over a recording medium, or the head is moved to a predetermined place near the periphery of the medium and held off the surface of the medium.
When the actuator receives an external shock during the rest of the disk apparatus at the predetermined place near the periphery of the disk, the actuator possibly moves from a refuge place to a data recording area on the medium, thereby damaging the surface of the data recording area due to a collision between the head and the surface of the medium. Here is another possibility of damaging the data recording area; when the apparatus starts working with the head held at the predetermined parking zone above the medium, sliding of the head on the surface of the medium sometimes damages the head and the surface of data area. On top of that, a collision between the actuator and other elements of the disk apparatus causes fatal damage to the other elements or the actuator. To avoid the foregoing damage, a conventional actuator has employed a latch device so that the actuator can be held at a given refuge place.
The conventional disk apparatus, of which actuator employs the latch device, is described hereinafter. The disk apparatus includes an actuator holding device. The actuator has a head at its first end, and a coil at its second end, which integrally forms a protrusion having an iron chip. This actuator is rotatably mounted on a rotary shaft. The coil and a permanent magnet rigidly mounted to a housing form a voice coil motor (VCM). The permanent magnet mounted to the housing confronts the iron chip of the actuator. The iron chip and the permanent magnet form the actuator holding device.
During the rest of the disk apparatus, the foregoing actuator holding device receives an electric current at the coil forming the VCM so that the actuator can move to a given refuge place. When the actuator approaches the refuge place, the iron chip is attracted by the permanent magnet, so that the actuator is fixed at the refuge place. This status protects the actuator against external force and prevents the actuator from moving because the actuator is fixed by magnetic attraction, so that data stored in a data recorded area of the recording medium and the head provided to the actuator are protected from careless movements of the actuator. This mechanism is disclosed in, e.g. Japanese Patent No. 2803693.
Another disk apparatus having an actuator holding device is also disclosed. This another one has a latch device formed of locking means and a solenoid coil, in addition to an actuator holding device similar to what is discussed above. The latch device has resilience so that it can engage with the actuator in vertical direction. To be more specific, the latch device comprises the following elements:                a plunger made of iron and moved by supplying an electric current to the solenoid coil;        a leaf spring having vertical stress and being moved vertically in response to the movement of the iron plunger;        a magnet having first magnetic force and placed under the plunger as first magnetic field supplying means; and        a VCM yoke having second magnetic force and placed above the plunger as second magnetic field supplying means. The solenoid coil generates magnetic force, which pushes up the plunger, when it receives a first electric current, so that the leaf spring moves upward.        
When a second electric current different from the first one is supplied, the solenoid coil generates magnetic force which push down the plunger, so that the leaf spring moves downward. On top of that, the first magnetic force of the magnet having downward magnetic force greater than upward stress of the leaf spring allows fixing the leaf spring at the lower position. In addition to the upward stress of the leaf spring, the second magnetic force of the VCM yoke allows attracting and fixing the leaf spring at the upper position.
When the disk apparatus having the foregoing structure is in operation, the plunger is attracted toward the magnet by the first magnetic force, and the leaf spring is urged downward by the plunger, so that the leaf spring is fixed at a height not prohibiting the actuator from moving. This is a lock-released status. On the other hand, when the disk apparatus is halted, the actuator is moved to a refuge place, i.e. a given locking place. Then the first electric current is supplied to the solenoid coil, which current is greater than the difference between the first magnetic force of the magnet and the stress of the leaf spring, and which current generates upward magnetic force. This first electric current moves the leaf spring upward and fixes it to the upper position. This is a locked status.
The current is supplied to the solenoid coil only when the status is changed from the lock released status to the locked status, and vice versa. However, when the leaf spring is fixed to the lower position or the upper position, namely, the actuator is in the lock released status or in the locked status, the current is not supplied to the solenoid coil. When the disk apparatus is halted, the leaf spring is fixed to the upper position by magnetic attraction from the iron chip and the permanent magnet. The actuator is thus locked at the refuge place. This is the locked status, which fixes the actuator riot only in horizontal direction but also in vertical direction, so that the actuator can be protected against external shocks and prevented from moving. Unexamined Japanese Patent Publication No. H08-221915 discloses one of the foregoing structures.
Another disk apparatus having an actuator holding device is described hereinafter. An actuator is rotatably provided on a swing shaft, and a head arm and a coil arm are placed confronting to each other with respect to the swing shaft in between. The disk apparatus structured above has the following features:                (1) The head arm comprises a carriage arm and a suspension arm which includes a tab having a protrusion for the head to take refuge in a ramp block, and a head slider having a magnetic head is mounted near to the tab.        (2) The coil arm having a voice coil mounted to its inner wall comprises an outer arm and an inner arm.        (3) The ramp block and an inertia latch device both provided to the refuge place of the actuator are housed in an enclosure.        (4) The ramp block fixed to the enclosure with screws has plural ramps protruded horizontally from a lateral face of ramp support, and the ramp has a complex plane including a first slope, a top plane, a second slope, a bottom plane and a third slope.        (5) The inertia latch device comprises the following elements:                    an inertia lever swinging on the swing shaft;            a latch lever swinging on another swing shaft; and            a spring for holding the latch lever at an arm open position.The inertia moment around the swing shaft of the inertia lever is set greater than that of the latch lever.                        (6) The inertia lever includes a balance arm and an inertia arm that has a first engaging protrusion to be engaged with the latch lever at a first engaging section and a second engaging protrusion to be engaged with the latch lever at a second engaging section.        (7) The latch lever includes a latch arm having two protrusions to be engaged with an active end of the spring, a positioning protrusion, and a latch protrusion, and it also includes an auxiliary arm. The positioning protrusion determines an actuator open position and an actuator latching position of the latch lever. The latch protrusion engages with a tip of the inner arm of the actuator for latching the actuator when the latch lever moves to the actuator latching position.        (8) The ramp block and the inertia latch device form an actuator locking device.        
The foregoing structure allows latching and locking the actuator at the refuge place, thereby preventing the head arm and the head slider from entering into a disk-mounted area. This structure is disclosed in, e.g. Unexamined Japanese Patent Publication No. H10-302418 and No. 2002-260356.
The foregoing disk apparatus including a conventional actuator holding device fixes the actuator at the refuge place by using attraction force of the iron chip provided to the actuator and the permanent magnet fixed to the housing. The actuator holding device structured above has thus comparatively strong resistance to a shock applied in the same direction as the swing direction of the actuator. However, it has comparatively weak resistance to a large shock or a shock having vertical components with respect to the swing direction. The holding device cannot function as a reliable holder when it receives a shock. Since the holding device needs the iron chip and the permanent magnet for holding the actuator at the refuge place, the number of elements forming the apparatus increases, which boosts the cost of the apparatus.
The disk apparatus having a conventional latch device of the actuator, which latch device is formed of locking means and a solenoid coil, includes an actuator holding device which comprises the following elements:                an iron chip provided to the actuator;        a permanent magnet provided to the housing;        a leaf spring for latching the actuator;        a magnet for fixing the leaf spring to the lower position;        a plunger for moving the leaf spring up and down; and        a solenoid coil for moving the plunger up and down.        
When the disk apparatus is halted, this structure allows moving the actuator to the refuge place, and moving the leaf spring upward in response to the vertical movement of the plunger, so that the leaf spring is put into a locked status. As a result, the actuator is locked at the refuge place.
The structure discussed above is thus strongly resistant to a comparably great shock. However, if it receives an extraordinary great shock applied along the moving direction of the plunger, upward stress of the leaf spring and the second magnetic force of the VCM yoke should be set resistive enough to the shock. For this purpose, the plunger should be moved downward in order to resist to the large resultant force of the upward stress and the second magnetic force, thereby putting the leaf spring in a lock released status. To achieve this mechanism, it is needed to supply a large current to the solenoid coil for generating great magnetic force. As a result, a large size solenoid coil is required.
On top of that, a space is needed for placing respective elements forming the actuator latch device which locks the actuator at the refuge place, so that it becomes difficult to downsize the disk apparatus, or save an electric current, i.e. save power of the disk apparatus. The actuator latch device needs a large number of elements, which boosts the cost of the apparatus, and at the same time, causes to lower the reliability.
The actuator of the foregoing disk apparatus is placed rotatably around the swing shaft, and is formed of a head arm and a coil arm opposed to each other with respect to the swing shaft placed in between. This disk apparatus includes the inertia latch device formed of the inertial lever, latch lever and spring. While the disk apparatus is halted, this structure allows the inertia lever to rotate, thereby rotating the latch lever anti-clockwise if the apparatus receives a comparatively great shock. In this case, regardless of a direction of torque working on the latch lever, the latch lever rotates anti-clockwise. The latch protrusion of the latch arm engages with a tip of the inner arm of the coil arm provided to the actuator moving from the refuge place, so that the actuator is latched.
To achieve the foregoing mechanism, the inertia moment of the inertia lever is set greater than that of the latch lever. The actuator holding device having the inertia latch device discussed above can minimize a dead zone to the shock, so that the reliability of the holding device increases. However, the inertia latch device needs a large number of elements and also a space for accommodating those elements. Those factors increase the cost of the device and resist downsizing the device.